Evidence for a high-level porphyritic intrusion below the Sunnyside epithermal vein deposit, Colorado

Mario A. Guzman; Thomas Monecke; T. James Reynolds; Thomas J. Casadevall

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USGS · 70243903

Evidence for a high-level porphyritic intrusion below the Sunnyside epithermal vein deposit, Colorado

Mario A. Guzman·Thomas Monecke·T. James Reynolds·Thomas J. Casadevall

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Abstract

High-temperature quartz veins were identified in drill core at ~600 m below the Sunnyside epithermal base and pre-cious metal deposit in southwestern Colorado. The veins consist of early anhedral quartz that shows a bluish ca-thodoluminescence emission and hosts heterogenous silicate melt inclusions. The early quartz is overgrown by a later generation of quartz that exhibits euhedral termina-tions with oscillatory growth zones showing a bright pink to purple cathodoluminescence emission. Both types of quartz are crosscut by ubiquitous planes of vapor-rich inclusions and some hypersaline liquid inclusions. In addi-tion, secondary planes of intermediate-density inclusions occur. The petrographic characteristics of the two quartz types are similar to those in ‘A’ and ‘B’ veins encountered in shallow- and intermediate-depth porphyry deposits. The relationships at Sunnyside imply that these high-temperature veins formed from magmatic-hydrothermal fluids derived from an intrusion located not far below the lowest level of drilling. Sunnyside appears to be a rare example of an epithermal deposit that is directly connected to a high-level porphyritic intrusion.

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Source-reported bounding extent: 36° to 40° latitude; -108° to -104° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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Mario A. Guzman, Thomas Monecke, T. James Reynolds, Thomas J. Casadevall. 2023. Evidence for a high-level porphyritic intrusion below the Sunnyside epithermal vein deposit, Colorado. https://pubs.usgs.gov/publication/70243903

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